High performance combustion engines attempt to utilize every reasonable advantage in extracting more utilizable horsepower and torque from the engine so long as the compromise in power or weight to achieve that horsepower is not excessive. Techniques to increase horsepower, for example, include reducing the exhaust pressure drop by either eliminating the muffler or tuning the exhaust port so that the pulsating exit of the exhaust gasses do not work to build the pressure drop. Superchargers and turbo chargers are another method of increasing horsepower by increasing the pressure into the combustion chambers, to add more fuel per stroke, and to extract more power upon each ignitive explosion.
In internal combustion engines, the piston downstroke transfers power from the ignitive explosion. The pressure of the explosion acts against the piston rod to turn the crank shaft, but also acts against the atmospheric or higher pressure in the crank case. Atmospheric pressure is normally expected to exist in the crank case, but slightly higher pressures can and do exist because the wiping sealing between the piston rings and combustion chamber are not perfect.
Elimination of even the atmospheric pressure in the crank case would eliminate by at least 14.696 pounds per square inch, the force opposing the power stroke of the piston. In addition, it would assist the piston's travel toward the crank shaft during the intake stroke when combustion air and fuel are being drawn into the combustion chamber. Admittedly, the piston would be working to compress the combustion chamber during the compression stroke and working to expel the exhaust gasses on the exhaust stroke against the reverse pull of a vacuum, but the greater criticality in withdrawing maximum power during the brief power stroke, as well as the advantage in drawing in combustants, significantly overcomes any compensation in either of the other two strokes where the piston would act against a vacuum developed in the crank case.
A vacuum in the crankcase can add, on average about 15% to the horsepower rating of the engine, depending upon the level of vacuum attainable. However, because the engine is not a perfectly sealed environment, a vacuum in the crank case is not maintainable as a static, pre-set condition. A vacuum draws in gasses from around the piston rings, as well as through the crank shaft and other imperfectly sealed surfaces between the crank case and available gasses which would defeat a pre-set vacuum.
In addition, the use of a conventional vacuum pump to try to achieve high vacuum is unworkable for several reasons. First, most of the positive displacement high vacuum pumps cannot provide a sufficient level expelled volume to be of sufficient use in keeping up with the crank case pressure or volume requirements. Second, the typical piston vacuum pump consumes significant energy since it too has a piston which is withdrawn against atmospheric pressure, only to compressively eliminate only a small amount of waste air at high vacuum for each stroke. Thirdly, the size and weight of a conventional vacuum unit is also prohibitive. One of the contributing factors to weight is the need to provide both sealing and lubricative bearing support of the shaft of the vacuum pump. Where a vacuum is had on one side of a shaft, the vacuum tends to draw lubricant and surrounding air and moisture into the vacuum pump. Repeated lubrication only results in lubricant contaminating the internals of the pump. Repeated lubrication in the high performance automotive environment is simply not a reasonable option.
What is therefore needed is a very light weight source of vacuum, which can move relatively high volumes of air from an evacuated crank shaft, but without loss of efficiency. The needed source of vacuum should also be relatively free of lubrication troubles, especially the problem of sucking the lubricant into the pump to leave the moving parts un-lubricated.